Researchers in western Idaho may have found some of the earliest evidence of human life in North America, indicating humans arrived to the area more than a thousand years earlier than previously thought.

Researchers at the Cooper’s Ferry archaeological site in western Idaho found evidence they say is linked to human activity dating back as far as 16,560 years ago. The study published Thursday in the journal Science suggests that humans migrated to the area not through a corridor in an ice sheet stretching from Alaska to the Pacific Northwest, but by traveling around the ice and along the coast of what is now Washington state.

“We found archaeological evidence that shows people were in western Idaho about 16,000 years ago,” said Oregon State University anthropology professor Loren Davis, the lead researcher on the study. “It shows people were south of the continental ice sheets from the last ice age before there was a corridor.”

The corridor, thought to have allowed humans to travel from the Yukon to Montana to the Dakotas, opened as early as 14,800 years ago. The theory that humans used this route has been challenged in recent years, as researchers have claimed to have found older artifacts in sites ranging from Chile to Oregon to Texas. Some scientists have been skeptical of these claims, though — as some are of Davis’ recent findings.

Ben Potter, an archaeology professor from the University of Alaska, Fairbanks, said he’s not yet convinced the oldest dated materials from the sitewere the result of human activity. To disprove the theory that humans used the corridor, researchers have to show there was human activity at the site before the corridor opened.

“It’s a very interesting site that raises interesting questions, but for me, it isn’t demonstrated beyond a reasonable doubt,” Potter said.

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Davis said he believes the evidence they found does suggest that people were living in the area before the corridor. While the oldest are pieces of animal bone, Davis said his team found charcoal with burned bone fragments, indicating the presence of a hearth, dating 14,670 to 15,195 years ago, as well as what they’ve interpreted to be a food-processing station from more than 16,000 years ago.

“We have the full array of the things you would want to see,” he said.

Archaeologist Donald Grayson, who is an emeritus professor at the University of Washington, told National Geographic that while he is typically skeptical of the dating of sites, he believes it’s “totally convincing” that Cooper’s Ferry artifacts date before those of the Clovis peoples believed to have entered North America through the corridor.

Davis partnered with researchers from Oxford University who used radiocarbon dating, which Davis called “the gold standard,” to determine the approximate ages of the artifacts. While there is always some uncertainty involved in dating artifacts, Davis said the researchers used ranges to account for this. From the lowest layer of the site that was studied, artifacts ranged from about 15,300 to 16,560 years old.

In the pit that the researchers believe to have been a food-processing station, they found what they think is a tooth from an extinct breed of horse dating back to the end of the last glacial period, as well as larger bone fragments. Davis said he believes the horse was butchered in the area, which would be a rare finding of direct human interaction with an extinct animal.

The U.S. Bureau of Land Management manages the Cooper’s Ferry site, which is an ancient village site of the Nez Perce Tribe called Nipéhe. Davis began studying the site in the 1990s.

Davis also found artifacts that he said resemble those found in sites in northeastern Asia, particularly in what is now Japan. Further work is being done to compare the artifacts, Davis said.

This story was updated to clarify Potter’s comments.